Biological calorimetry is a field primarily concerned with the measurement of the heat effects produced in biochemical processes. There are two categories of reaction processes of interest which produce heat while reacting.
The first category of reactions are those between two chemical entities (reactants M and X) to produce a third species (product MX), such as the binding of a drug to a protein molecule to produce a drug/protein complex. This binding (interriolecular) reaction is depicted by the chemical reaction equation, M+X.fwdarw.MX.
The second category of reactions are those that result in a transformation of the molecular state of a substance (from the reactant state M to the product state M') due to an increase in temperature, such as the unfolding of proteins and various nucleic acid structures or the melting of a lipid suspension. This unfolding (intramolecular) reaction is depicted by the chemical reaction equation, M.fwdarw.M'.
Typically, one measures the heat effects for binding (intermolecular) reactions (i.e. the first category) using a conventional calorimeter by mixing the reactants in a "reaction chamber" while monitoring the temperature change in the reaction chamber with a thermometer or a thermoelectric sensor. The temperature or voltage change is converted into a unit of heat by calibrating the calorimeter against a standard heat effect generated by the passage of electric current through a resistor placed in the reaction chamber.
Similarly, one typically measures the heat effect due to unfolding (intramolecular) reactions (i.e. the second category) using a scanning calorimeter, which measures the heat effect produced upon increasing the temperature of the contents of a reaction chamber.
Conventional methods of thermodynamic data collection for chemical reactions tend to be very repetitive and time consuming. Using conventional methods, the time required to determine the equilibrium constant and enthalpy of the unfolding of a protein at eight different values of PH can take between 3 to 8 days. Another limitation of conventional methods is that two different devices are needed to measure both binding (intermolecular) and unfolding (intramolecular) reactions. In addition, the accuracy of a conventional reaction calorimeter is limited by heat effects caused by stirring the reactants in the reaction chamber. The use of conventional scanning calorimeters can be very time consuming because scanning calorimeters tend to require lengthy temperature equilibrium periods.
Therefore, a need exists for a single device which can determine heat effects for both binding (intermolecular) and unfolding (intramolecular) reactions with increased accuracy and in less time than traditional methods.